Recently, a greenhouse effect caused by CO2 is noted as one reason of having global warming phenomenon. Thus, a solution for protecting earth and environment is urgently needed all over the world. As a source for generating CO2, there is every human activity which is involved with combustion of fossil fuel, and thus a demand for inhibited emission tends to increase more than ever. Accordingly, for power generating facilities like thermoelectric power station which uses a large amount of fossil fuel, extensive studies are made on a method of removing and recovering CO2 in flue gas by bringing flue gas from a boiler into contact with an amine-based CO2 absorbent and a method of storing recovered CO2 without release to air. Furthermore, as a process used for removing and recovering CO2 in flue gas by using an CO2 absorbent, there is a process in which flue gas is brought into contact with a CO2 absorbent in an absorber, the absorbent after absorption of CO2 is heated in a regenerator, and with release of CO2, the absorbent is regenerated and recycled to the absorber for reuse (for example, see Patent Literature 1).
According to a method of removing and recovering CO2 from CO2 containing gas like flue gas by using an CO2 absorbent and the process described above, the process is annexed to facilities for combustion, and thus the cost related to the operation should be reduced as much as possible. Among the above processes, the regeneration process particularly consumes a large amount of heat energy, and thus it needs to be provided as a process which can save the energy as much as possible.
Accordingly, a suggestion has been made in a related art that part of a semi-lean solution is discharged to the outside from a regenerator for heat exchange with a lean solution in a heat exchanger, subjected to heat exchange with steam condensate in a heat exchanger, and returned to a lower side than the extraction area, and by increasing the temperature of a semi lean solution fed to the bottom side of a regenerator, steam consumption amount is reduced (for example, see Patent Literature 2 (Example 8 and FIG. 17)).